List custom domains

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Annotations already declare readOnlyHint, idempotentHint, and destructiveHint=false, covering the safety profile. With no output schema, the description carries the return-shape burden and does so well by listing the fields returned. It omits pagination/ordering behavior, which is a minor gap for a list tool.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Is the description appropriately sized, front-loaded, and free of redundancy?

Two sentences, front-loaded with the resource and field enumeration before the downstream-tool pointer. Every clause earns its place and nothing is redundant.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

For a zero-parameter read-only list with no output schema, the description supplies the returned fields and points to the tools that consume the ids. It lacks pagination or result-ordering details, but is otherwise sufficient to invoke and use correctly.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

The tool takes no parameters, so there is no parameter semantics to clarify — the baseline of 4 applies. The description doesn't need to document inputs and correctly focuses on output shape instead.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Does the description clearly state what the tool does and how it differs from similar tools?

States a specific verb (List) plus resource (custom domains) and enumerates the returned fields, including id, verification status, and recipient mailboxes. This distinguishes it clearly from siblings like alias_domains_list and mailbox_list without opening either schema.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Does the description explain when to use this tool, when not to, or what alternatives exist?

The second sentence names the downstream tools (custom_domain_update, custom_domain_trash_list) and conditions their use on ids returned here, which is clear workflow context. However, it doesn't state when to choose this over alias_domains_list or other list tools, so no explicit alternatives/exclusions are given.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.